Control of the load distribution of a plurality of generator units or other energy transmission units supplying a common load



1945- P. G. KAUFMANN 2,366,

CONTRO F THE LOAD DISTRIBUTION OF PLURALITIES GENERATOR UNITS OTHER ENERGY TRANSMISS UNITS SUPPLY COMMON LOA Filed t. 2, 1942 7 Sheepset 1 1 27 3 ad %ae,?

9, 1945- P. G. KAUFMANN 2,366,968

CONTROL OF THE LOAD DISTRIBUTION OF PLURALITIES OF GENERATOR UNITS OR OTHER ENERGY TRANSMISSION UNITS SUPPLYING COMMON LO Filed Sept. 2, 1942 7 Sheetsest 2 W Jan. 9, 1945. P KAUFMANN 2,366,968 CONTROL OF THE LOAD DISTRIBUTION OF PLURALITIES 0F GENERATOR UNITS OR OTHER ENERGY TRANSMISSION UNITS SUPPLYING COMMON LOADS Filed Sept. 2, 1942 7 Sheets-Sheet 3 Jan. 9, 1945.- P K UFMANN 2,366,968 CONTROL OF THE LOAD DISTRIBUTION OF PLURALITIES OF GENERATOR UNITS OR OTHER ENERGY TRANSMISSION UNITS SUPPLYING COMMON LOADS Filed Sept. 2, 1942 '7 Sheets$heet 4 o so is I 63 I 63 1945- P. e. KAUFMANN- CONTROL OF THE LOAD DISTRIBUTION-0F PLURALITIES OF GENERATOR UNITS- OR OTHER ENERGY TRANSMISSION UNITS SUPPLYING COMMON LOADS Filed Sept. 2, 1942 7 Sheets-Sheet 5 l ashes Slo.

Jan. 9, 1945. P KA 2,366,968 CONTROL OF THE LOAD DISTRIBUTION OF PLURALITIES 0F GENERATOR UNITS OR OTHER ENERGY TRANSMISSION UNITS SUPPLYING COMMON LOADS Filed Sept. 2, 1942 7 Sheets-Sheet 6 Jan. 9, 1945. P, KAUFMANN 2,366,968 coNTRoL OF THE LOAD DISTRIBUTION OF PLURALITIES OF GENERATOR UNITS OR OTHER ENERGY TRANSMISSION UNITS SUPPLYING COMMON LOADS Filed Sept. 2, 1942 7 Sheets-Sheet 7 OUTPUT Flql2 m I l 29 C14 m 30 U4 Al Patented Jan. 9, 1945 CONTROL OF THE LOAD DISTRIBUTION OF A PLURALITY OF GENERATOR UNITS OR OTHER ENERGY TRANSMISSION UNITS SUPPLYING A COMMON LOAD Paul George Kaufmann, London, England Application September 2, 1942, Serial No. 457,094 In Great Britain September 3, 1941 35 Claims.

This invention relates to the control of the load distribution of a plurality of generator units or other energy transmission units supplying a common load.

The primary object of the invention is the provision of means whereby such load distribution may be so controlled that maximum efficiency will be obtained-that is to say, that, for any given total load, the total input, or the sum of the inputs of the several units, will be a minimum.

In accordance with the invention I provide means for either efiecting, or indicating, the control of the several units, such that, at any given moment, said units operate on respective points of their characteristic, or loadinput, curves which are of the same slope. This is to say, said units operate so that they all require the same change of input for a given change of output.

In some cases where other variables have to be taken account of, the above relationship, viz. that the units operate on points of their characteristic curves which are of the same slope, may be modified in order to compensate for such other variables. An example of this is when a number of electrical power units supplying a common load are interconnected by tie lines, and the loss of energy in said tie lines is such that it ought not to be ignored. The invention has therefore as a further object the provision of means for modifying the said relationship so as to compensate for such other variables.

The invention has for a further object the provision of means for determining how many and which out of a'number of units should for best efliciency be in operation for any given total load,

the units which are in operation having their loads distributed as above described.

Many other objects and advantages of the invention will appear hereinafter,

It will be appreciated that the variables employed as load and input in the said characteristic curves will depend, even in thesame type of unit, on the type of efficiency required. For example, in the case of steam generators, it would usually be a maximum thermal efliciency which is required, and the load and input could be measured in B. t. u. per hour, in the steam generated and in the coal consumed respectively, but, if different kinds of fuel were' employed in the several generators, it might be preferred to meas ure the input in terms of the cost of coal consumed per hour and thus a maximum financial efllciency (but not necessarily'a maximum thermal efilciency) would be obtained.

clearly understood a number of arrangements in accordance therewith will now be described, reference being made to the accompanying drawings, wherein:

Figure 1 is a somewhat schematic and diagrammatlc view of a system in which the invention is applied to the control of load distribution of a plurality of steam generators supplying a common load.

Figure 2 is a perspective view to an enlarged scale of the devices illustrated in Figure 1 for determining the output distribution of the respective steam generators.

Figure 3 is a perspective view of an alternative form of the devices for determining the output distribution of the respective steam generators.

Figure 4 is a schematic and diagrammatic view of a system in which the invention is applied to the control of the load distribution of a plurality In order that the invention may be the more of electric generator units supplying a common load.

Figure 5 is a schematic view of a system in which the invention is applied to the control of the load distribution of a plurality of electric generator units supplying a common load and in which the generator units are divided into groups at stations which may be at a considerable distance from one another.

Figure 6 is a circuit diagram illustrating a portion of the system of Figure 5.

Figure '7 is a schematic view of a system which is similar to that of Figure 5, save that the stations are interconnected and the transmission losses between them are taken account of in determining the load distribution of the generator units.

Figure 8 is a circuit diagram illustrating a portion of the system of Figure 7.

Figure 9 illustrates a modification which may be applied t the system of Figures 7 and 8.

Figure 10 is a graph indicating when less than all of a number of power units supplying a common load should be used, for highest efllciency; and

Figures 11 and 12 together illustrate an apparatus whereby the indications of the graph of Figure 10 may be implemented.

Referring first to Figures 1 and 2, a number of steam generators I (only one of which is shown) supply a common steam main 2. The inputs to the respective generators l are controlled in accordance with the positions of respective longitudinally slidable parallel rods 3. The rods 3 are all moved simultaneously in one or other direction according to the pressure variations in the steam main 2 in such a way that the pressure in said steam main 2 is retained approximately constant at a given value despite variation in the total demand. The means by which the rods 3 are moved in one or other direction to increase and decrease the respective generator inputs are such that the relative positions of said rods 3 and the relative inputs of said generators l, are always so correlated that the several generators at any given moment, always work on points of their respective input-output characteristic curves which are of the same slope. In other words the generators I operate so that they all require the same change of input for a given change of output and in this way it is ensured that the most efiicient load distribution of the several generators is obtained.

Referring now more paricularly to Figure 2 which illustrates one means by which the movement of the rods 3 is effected, the same illustrates a number of parallel stationary plates 4 having curved slots 5 formed in them the centre lines of which conform to the characteristic curves of the several generators l and are arranged with their output ordinates parallel to the direction of movement of the rods 3. Associated with these plates 4 are a. number of elongated plates 6 having rectilinear slots 1 formed in them. Each plate 6 rests flat against the corresponding plate 4. A roller 8 located jointly in each pair of slots 5 and l maintains the slots together at one point, and the engagement of a straight edge 9 of each plate 6, which straight edge is parallel to the slot 1 with a curved shoulder l formed on the corresponding plate 4, which curved shoulder is parallel to the centre line of slot 5, insures that the centre lines of the rectilinear slots 1 will always betangential to the centre lines of the respective curved slots 5.

The elongated plates 6 are adapted to be rotated jointly, with their slots 1 remaining parallel to each other, according to variations in pressure of the steam main 2. In so rotating, the slots 1 will be constrained, as stated, to remain tangential to the respective slots and it will be clear that the rollers 8 will be constrained always to take up positions at the respective tangent points. The rods 3 are moved longitudinally according to those components of the movements of the respective rollers 8 which are parallel to the output ordinates of the slots 5 and the actual output of the generators are so correlated to the position of the rods 3 that they are always equal to the outputs indicated by the output ordinates of the respective curves 5 at the points occupied by the rollers 8. It therefore follows that the several generators always work on points of their characteristic curves represented by the points occupied by the rollers 3 in the slots 5, and, as the slots 1 are always tangential to the respective slots 5 at the said points occupied by the rollers 8 and are parallel to each other, the rollers 8 are always at points of the slots 5 which are of the same slope. In other words the generators always operate on points of their characteristic curves which are of the same slope.

The means by which the plates 6 are rotated jointly with their slots remaining parallel to each other comprise a rigid rectangular frame having members H, l2, l3 and M and adapted to be rotated about an axis |5 at right angles to the planes of the plates 4 and passing through the mid points of the opposite members I and I2. Each elongated plate 6 is pivoted at one and r to one end of a link I whose other end is pivoted to the frame member l3 and said plate 6 is pivoted at its other end to one end of a, link I! whose other end is pivoted to'the frame member l4. The links l6 and H are of the same length and the distance between the frame members I3 and I4 is equal to the length of each plate 8. Thus each plate 5 is constrained always to remain parallel to the plane of the frame l2, l3, I4 while being free to move with its.slot l tangential to the slot 5 as heretofore described. As all the plates 5 are always parallel to the plane of the frame they are always parallel to each other.

For mounting said frame for rotation about the axis 'l5, short shafts i3 (only one of which is seen) project rigidly from the mid points or the frame members H and I2 and bear on respective bearings IS. The rotation of the frame isefi'ected through the medium of a lever 20 rigidly mounted on one of the shafts III.

In order to move the rods 3 as stated according to the components of the movements of the rollers 3 parallel to the output ordinates of the slots 5, each roller 8 is mounted at one end of a rod 2| whose orientation is always parallel to the output ordinates of the slot 5 and whose other end has rollers 22 mounted thereon which bear against a bar 23 parallel to the plane of the plate 4 and at right angles to said md 2| and which is capable of moving in a sense longitudinally of said rod 2| without changing its orientation. The respective rod 3 has rollers 26 mounted at one end thereof which bear against said bar 23 at the side opposite to the rollers 22. The rod 3 is biased by means of a spring 25 so that the rollers 24 press against the bar 23 and this presses the bar 23 against the rollers 22 and thus the longitudinal position of the rod 3 and the rod 2| is determined by that component of the position of the roller 8 which is parallel to the output ordinates of the slot 5. As the roller 8 moves in the slot 5 the rod 2| will move with it but only the component of such movement which is parallel to the output ordinates of the slot 5 will effect movement of the bar 23 and therefore of the rod 3.

It will be appreciated from the drawings that the spacing apart of the rollers 22 is such that the rod 2| automatically remains at right angles to the bar 23 and therefore parallel to the output ordinates of the slot 5. The rods 3 will be mounted for longitudinal movement in bearings not shown.

To enable each bar 23 to have the parallel movement described, it is pivoted at its two ends to the ends of respective links 26 whose other ends are pivoted to fixed points, the links 26 being of equal length and the length of the bar 23 being equal to the distance between the fixed points.

The detailed manner in which the lever 20 is moved in accordance with variations in the pressure within the steam main 2 forms no part of the present invention and it has therefore not been deemed necessary to illustrate this other than diagrammatically. Any known form of control, such as the pressure regulator 2a, can be employed which ensures that the pressure in said steam main 2 remains at approximately the desired value.

Likewise the manner in which the input of each generator I is controlled so as to give an output corresponding to the position of the respective rod 3 may be according to any known practice. In the arrangement illustrated in FIG- ure 1 this control is eii'ected electrically through the medium of respective sliding contact rheostats 21 whose sliding contacts are connected to the respective rods 3 so that the resistance of said rheostats vary according to the positions of the rods 3, and therefore represent the desired values of the outputs of the respective generators.

Each rheostat 21 is caused to control the input of the respective generator I by being balanced against a rheostat 28 whose resistance is adapted to be automatically varied soas to keep its value equal to that of the rheostat 21 by means of a reversible electric motor 29 which also controls the generator input, represented diagrammatically by the damper 30 controlling the air supply to the furnace 3 l Thus the two rheostats 21 and 28 are connected as shown to form adjacent arms of a Wheatstone bridge whose other two arms are constituted by fixed resistances 32 and 33 of equal value. .A small source of voltage 34 is connected between the point of junction of the rheostats 21 and 28 and the point of junction of the resistances 32 and 33 and a galvanometer 35 is connected between the remaining two points of junction as shown. The electric motor 29 has three terminals 38, 31 and 38 and is driven in one direction when a source of power 39 is connected across the terminals 38 and 31, and in the other directions when said source of power is connected across the terminals 36 and 38. A switch member 40 is coupled to the needle of the galvanometer 35, and is adapted to connect the source of power 39 across the terminals 36, 31 or 36, 38 according to whether said needle moves in one or other direction from the neutral. When said needle is at the neutral position said motor circuit is broken.

From the above it will be clear that when the two rheostats 21 and 28 have a different value, a potential will exist across the terminals of the galvanometer and the switch member 40 will connect the source of power 39 to the motor 29 to drive it, and therefore the sliding contact of the rheostat 28, in one or other direction. The arrangement is such that said motor is driven in the direction to equalise the value of the rheostat 28 to that of the rheostat 21. Thus the values of said rheostats 21 and 28 will always be equal and the position of the sliding contact of the rheostat 28 (and therefore the position of the damper 38) will be a function of the resistance of said rheostat 21. The rheostat 28 will be so wound that the actual input to the generator will be such as to give the output represented by the position of the rod 3.

'said generator to remain at its maximum or minimum load, the loads of the other generators being distributed as heretofore described. This requirement may be taken care of by arranging that when any roller 8 reaches that end of the respective slot 5 which represents the point, of maximum or minimum input and output of the respective generator, the respective elongated p ate 6 will be free to continue turning about the roller 8 without its slot 1 being tangent to the slot 5, the roller 8 thus remaining stationary at the end of the slot and the load of the respective generator remaining constant at its maximum or minimum value. Inthe device illustrated in Figure 2 it will be seen that this is eifected by cutting away the curved shoulder II) at both ends, as at 4|, to permit the plate 8 to rotate out of the tangential position as stated.

The above described apparatus is simple and illustrates clearly the theory of the invention. It will be seen that precisely the same control of the respective steam generator inputs can be obtained by the use of simple cams, for example cams of varying radius on a common cam shaft. Such an arrangement is illustrated in Figure 3. This fig ure shows cams 42 of varying radius mounted on 7 a common cam shaft 43 and engaging at their At this point it may be mentioned that the slots 5 could have been so located that the rods 3 moved according to the input ordinates and riot the load ordinates. This would have meant winding each rheostat 28 so that the actual input to the generator would be that represented by the position of the rod 3. This would appear to be the more logical method as it is actually the input which is controlled, but in this art one usually thinks in terms of generator output and it is therefore preferred to arrange'the slots in the manner first described.

It may sometimes happen that the total output reaches a point at which the output required of one (or more) of the generators is beyond either the upper or the lower limit to which the utput of said generator is capable of reaching. In this case the most economical arrangement is for the peripheries with rollers 44 mounted at the ends of longitudinally slidable rods 3a which are radial with respect to the cam shaft and are biasedby means of respective springs 45 so that the rollers 44 press against the cam peripheries. The cam shaft 43 has a lever 20a rigidly mounted on it which corresponds to the lever 28 of the preced ing embodiment and is actuated in the same manner in accordance with the pressure variation in the steam main 2. The rods 3a correspond with the rods 3 of the preceding embodiment and their longitudinal position controls the inputs to the respective generators through rheostats 21 in the same manner. It will be seen that all that is necessary to obtain exactly the same control as in the preceding embodiment is for the radii of each cam 42 from the axis of the cam shaft 43 to represent the output ordinates (or a definite function of said output ordinates) and the angular positions of said radii around said axis to represent the slopes corresponding to said output ordinates, of the characteristic curve of the respective generator. The angular relation of the cams 42 to each other and to the rollers 44 will of course be such that, at any given time the operative radii of the several cams would all correspond to the same angle about the cam shaft axis, or in other words that the operative load ordinates of the several characteristic curves correspond to a common slope of said characteristic curves. Obviously the simplest way is for the rollers all to be in line as shown and the angles of the radii of the several cams to be measured from the same datum angle.

To take care of the point mentioned in connection with the preceding embodiment, that the total output may reach a point at which the output required of one (or more) of the generators is beyond either limit which the output of said generator is capable of reaching, all that is necessary in the present embodiment is to continue the cam surface at constant radius from the point corresponding to the point of maximum and minimum output of the generator. Further rotation of the cam will thus keep the generator at its said maximum or minimum load, and the condition will be as described in connection with the preceding embodiment.

Referring now to Figure 4 this illustrates an arrangement in which, inplace of the co-operating slots of Figure 2 and the cams of Figure 3 variably wound sliding contact rheostats 45 are employed. This figure moreover illustrates the invention as applied to the control of a number of electrical generator sets supplying a common load circuit 41. One of said electrical generator sets comprising a turbine 48 driving an alternator 49 is illustrated. Each of the sliding contact rheostats 46 is so wound that, if the position of its sliding contact 50 represents the slope of the characteristic curve of the respective generator, the resistance of said rheostat is proportional to or is a definite function of the load ordinate of the characteristic curve corresponding to that slope. The sliding contacts 50 are mounted on a common shaft so as to move together with their positions all simultaneously representing the same slope on the respective characteristic curves. The respective resistances of the rheostats 46 therefore represent corresponding values of the loads of the respective generators for the desired load distribution.

The resistance values of the rheostats 46 therefore correspond to the resistance values of the rheostats 21 of Figure 1 and are caused to control the input to the generator units in the same way. Thus each rheostat 46 is connected in a Wheatstone bridge with a rheostat 52 and resistances 53, 54, and said Wheatstone bridge has a source of voltage 55 and a galvanometer 56 connected to it, said galvanometer controlling a switch element 51 to thereby control the energisation for reverse directions of a motor 58. These references 52, 53, 54, 55, 56, 5! and 58 correspond exactly to the references 28, 32, 33, 34, 35, 40 and 29 and no further description is deemed necessary. In the present instance the control of the input of the generator unit by the motor 58 is effected through controlling the compression of the speed adjustment spring 59 of a centrifugal governor '50 which controls a valve 6! in the supply pipe 62 of the turbine 48. In similar manner to Figure 1 each rheostat 52 will be wound to ensure that the generator unit gives the correct output represented by the corresponding resistance 46.

It will be appreciated that as all alternators connected to the same load circuit necessarily run at the same speed the adjustment of spring 59 results in the variation not of the speed but of the output of the respective generating set relative to the other sets.

To take care of the case, referred to in the preceding embodiments, in which the load required by any given unit is greater or less than that which said unit is capable of supplying, each sliding contact 50 when it reaches the extremity of the resistance 45 can continue moving on a segment 63 of zero resistance so that the corresponding generator will remain with its load unchanged at its maximum or minimum value.

Obviously the maximum and minimum resistance of the rheostat 46 and therefore the maximum and minimum output of the corresponding generator set can be made adjustable.

In a manner analogous to Figure l the shaft 5| is automatically rotated in reverse directions in such a way as to maintain constant the frequency or some other condition of the load circuit 41. Thus a frequency controller 54, or controller responsive to such other condition, is connected to the load circuit 41 as indicated, and this frequency controller controls a switch ll in such a way that according as the frequency in the circuit 41 varies in one or other direction from the required frequency, a motor Cl driving the shaft 5| is connected for operation in one or other direction to a source of power 51.

It will be appreciated that. in all of the embodiments hereinbefore described, as the magnitudes representing the slopes of the several characteristic curves are, at any one time, always kept identical for all the units, the actual scale'of these magnitudes can be chosen at will without affecting the results. It is therefore possible to use a logarithmic scale for these magnitudes. In the case of the cams 42 illustrated in Figure 3 this would mean that the angular positions of the radii of each cam would vary as the logarithm of the slopes of the characteristic curve of the respective generator corresponding to the output ordinates of said curve represented by said radii. In the case of the rheostats 46 illustrated in Figure 4 it would mean that the longitudinal positions of the sliding contact 50 of each rheostat would vary as the logarithm of the slopes of the characteristic curve of the respective generator unit corresponding to the output ordinates of said curve represented by the resistances of said rheostat at said longitudinal positions.

In some cases the input values for any one generator may be altered in relation to the corresponding output values by being multiplied by a factor K. For example, if the inputs be measured in terms of cost of the fuel and the outputs in terms of B. t. u.s, and if the price of the fuel of one of the generators were to alter by the factor K, this means that, for each output value the corresponding input value would be altered by the factor K. Accordingly the values of the slopes of the characteristic curve would be effected in the same way, each value of the slope being multiplied by the factor K. If the slopes of the characteristic curve in the cam 42 or rheostat 46 were represented on a linear or any other scale except a logarithmic one, such alteration of the input and slope values would require the replacement of the respective cam or rheostat by a. new one. With a logarithmic scale, however, the necessary adjustment can be made simply by rotating the cam 42 around its shaft 43 or by shifting the rheostat 46 about the axis of the shaft 5| by an amount equal to log K.

In order therefore to compensate for such changes of the input values, a logarithmic scale is used for the rheostat slider positions or cam angles representing the characteristic slopes, and means are provided to adjust bodily the relative position of each cam or rheostat with respect to the other cams or rheostats suitable scales being provided indicating various values of the factor K to which such adjustments correspond.

Referring now to Figure 5 this shows, in a schematic manner a system in which a plurality of electrical generator units 68 supply a common load circuit indicated by the line 69 and these generator units are located in groups at a number of different regional stations 10 which are a long distance apart. If the load distribution oi all the generator units 68 were controlled in any of the ways heretofore described from a single location, that location would have to be very far distant from most of the generator units, and therefore control circuits from the rheostats 21 or 46 as the case may be to the motors 29 or 58. would have to be very extended. This is inconaseacee venient. For example it renders impracticable the-Wheatstone bridge form of control illustrated in Figures 1 and 4. In the arrangement illustrated in Figure therefore the load distribution of the generator units 68 of each group is controlled from its own regional station in the way'described, say, in Figure 4 and the load distribution between the several groups is controlled in an analogous manner, from a master control station H, each group being at the master control station, treated as one unit, and the inputoutput characteristic of the group as a whole being taken account of at the master control station in determining the correct load distribution between said several groups.

In this way only a limited number of very long control circuits have to be employed, viz. those extending from the master control station H to the several regional stations Ill.

Figure 6 illustrates the control circuit from the master control station to one of the regional stations (say the centre regional station of Figure 5 at which there are only two generator units).

Thus referring to Figure 6 there are, at the master control station a plurality of sliding contact rheostats 12 corresponding to the several regional stations 1. e. to the groups of generator units, each of said rheostats being so wound that, if the position of its sliding contact I3 represents the slope of the characteristic curve of the respective group of generator units taken as a whole, its resistance is proportional to, or is a definite function of, the load ordinate of the characteristic curve corresponding to that slope, The sliding contacts '13 are mounted on a common shaft 14 so as to move together, with their positions all simultaneously representing the same slope on the respective characteristic curves. The respective resistances of the rheostats 12 therefore represent corresponding values of the loads of the respective groups of generator units, for the desired load distribution, in just the same way as the resistances of the rheostats 46 of Figure 4 represent corresponding values of the loads of the individual generator units 48, 49.

The individual generator units of each group have their load distribution controlled at the re-- spective regional station by sliding contact rheostats 46a having sliding contacts 50a mounted on a shaft sic in exactly the same way in which the individual units of Figure 4 have their load distribution controlled by sliding contact rheostats 46 having sliding contacts 50 mounted on a shaft 5|.

Obviously the input to the group of generator units as a whole is controlled by rotation of the shaft 5m, and it is necessary that this rotation shall be controlled in accordance with the resistance value of the corresponding rheostat I2 at the master control station in such a way that the output of the group as a whole shall correspond to the resistance value of said rheostat 12. This control is efiected in the following way:

A small source of power 15 is connected in a series circuit with the several rheostats 12 at the master control station, and, in this circuit, is

connected a compensating device for ensuring given constant current despite variation of the resistance values of the several rheostats. Such a compensating device, which is well known, may comprise an ammeter l6 and rheostat 11 in series in the circuit, and means whereby said rheostat II increases or decreases its resistance value so long as the ammeter needle reads above or below the said given constant current. Therefore the voltage across each rheostat 12 is a measure of its resistance value. Each rheostat 12 has connected across it a volt meter 18 and the readings of said volt meter are a measure of the resistance value of said rheostat 12. Each volt meter 18 controls a sending device 1.9 which in turn controls a receiving device 80 at the regional control station in such a way that, said receiving device 80 develops the voltage indicated by the volt meter 18 and this voltage is impressed across the ends of a resistance 8!. Sending and receiving devices 19 and 80 which function as stated are known in the art and no description of them is deemed necessary.

At the regional control station is a small source of power 82 connected in a series circuit with the several rheostats 4611 through a compensating device ensuring given constant current, which compensating device may consist of an ammeter 83 and 'variable rheostat 84 which operate in the sam way as the ammeter l6 and rheostat ll. Therefore the total voltage across the rheostats 46a is proportional to the total resistance of said rheostats and therefore represents the total output allotted to the generator units corresponding to said rheostats, that is, the total output of the group of generators at that station. The shaft 51a is rotated until this voltage is equal to the voltage across the resistance 8i which, as heretofore demonstrated, represents the resistance value of the corresponding rheostat 12 at the master control station.

Thus the resistance of the rheostat 12 will corresponding to the total resistance of the rheostats 46a at the corresponding regional control station and the required condition is accordingly obtained.

For thus rotating the shaft 5la until the total voltage across the rheostats 46a is equal to the voltage across the resistance 8|, said resistance 8i is connected, in series with a galvanometer 85, across said rheostats 46a in such a sense that the voltage across it opposes the voltage across said rheostats So. When these two opposing voltages therefore are equal, the needle of the galvanometer 85 will register zero, and said needle will move in one or other direction according to whether one or other of said opposing voltages is the greater. Each needle controls a switch member 86 in a manner exactly analogous to the switch member 40 of Figure 1, so that a motor 81 which is coupled to the shaft 51a is driven from a source 88 in one or other direction according to the direction of movement of the needle of the galvanometer so as to equalise the aforesaid two voltages andreturn said needle to zero when said motor is cut off from said source.

In" order that the. whole system shall be controlled so that the frequency and therefore the voltage of the load circuit 69 (Figure 5) shall be constant, the shaft H of the rheostats at the master control station is rotated in one or other direction when the frequency is above or below the required value, in such a way as to restore said frequency to the required value. To this end a frequency controller 89 (Figure 5) which is connected to the load circuit 69, controls a switch member 9|! which in turn controls the connection to a source 91 for reversing motor 92 which drives said shaft H, the action being exactly the same as that ofthe corresponding parts 84, 65, B1 and 66 of Figure 4. The references 92 and 14 are shown in both Figures 5 and 6.

As the voltage across each rheostat 12 at the master control station ll gives a measure of the total output allotted to the several power units 68 at the regional station I corresponding to said rheostat I2 the total voltage across the several rheostats I2 will give a measure of the total output required of all the power units 98 in the system. Therefore by connecting a volt meter 93 across all of the rheostats I2 2. measure is obtained of the total output of the whole system, required to maintain the frequency at its normal value, which is of course equal to the demand on the whole system. To be aware, at any moment, at th master control station of the total load of the system is a great advantage.

Obviously the cascading system described with reference to Figures 5 and 6, in which the individual generator sets are controlled from regional control stations, which regional control stations are again controlled from a master control station, could be extended indefinitely by interposing stations controlling groups of regional control stations and so on.

Referring now to Figure 7 this illustrates schematically an arrangement which is similar to that of Figure 5 save that the groups of power units are interconnected by means of tie bars in which losses take place which cannot be ignored. As in Figure 5 the references 69 designate the power units, the references "I0 the regional control stations and the references II the master control station. The several power units 69 at each regional control station lO are connected together by means of a station busbar 94 which serves to supply the regional consumers, indicated diagrammatically at 95, and the several busbars 94 are interconnected by means of tie lines 96.

In order to compensate for the losses in the tie lines 96, each regional control station has a number of wattmeters 91 connected in its respective tie lines 96 close to the busbar 94 of said station. These wattmeters 9'! measure the value and direction of the power outgoing from, or incoming to, their respective busbars by the several tie lines. The readings of the several wattmeters 91 appertaining to each bus bar (in the present instance two in number) multiplied by the corresponding tie line coeilicient k and the reciprocal value of the square of the cos o of the transmitted power, are totalised and transmitted by a telemeter sender 98 to a telemeter receiver 99 located at the master control station II. It the power sent out from, or received by, a given busbar 94 by way of any tie line 96 is g, taken positive when sent out and negative when received, the sender 98 transmits the value to the receiver 99. The several receivers 99 influence the distributor at the master control station H in a manner which will now be described with reference to Figure 8. Said master load distributor is controlled by a frequency regulator 89 connected to some point of the power network in exactly the same way as the master load distributor of Figure 5 in such a way as to maintain substantially constant the frequency of the load.

Referring now to Figure 8 this illustrates in detail the master load distributor at the master control station II of Figure 7. Figure 8 corresponds to the upper part of Figure 6 and shows rheostats I2 having sliding contacts I3 and mounted on a common shaft H a, source of power 15 and an associated compensating device 16, 11 connected in series with said rheostats, voltmeters I8 connected across said rheostats, and

sending device I9 associated with the respective voltmeters 19 each for influencing the load distributor (not shown in Figure 8) at the respective regional control station, all exactly in the manner described in connection with Figure 6. Figure 8 also shows a motor 92 for driving the shaft 14 (under the control of the frequency controller 09) in the same way as described in Figure 6. Also the common voltmeter 93 for indicating at any moment the total load of the system. Figure 8 diifers from Figure 6 only in the means for influencing the several rheostats 12 by the respective telemeter receivers 99 (shown in both Figures 7 and 8).

Thus the resistances I2 are wound on a lossrithmic scale, as heretofore described, and each resistance I2 is mounted upon a ring I00 which is rotatable so that said resistance is capable of being adjusted about the shaft 14 on which its sliding contact I3 is mounted. When the rings I00 are at their normal or central positions (representing no load on the tie lines 99 of Figure 7) everything is exactly the same as in Figure 6, the positions of the sliding contacts I3 corresponding to equal slope values of the characteristic curves of the groups of power units at the respective regional control stations.

The values received, as heretofore described, by the telemeter receivers 99 are transformed by each of said receivers 99 into a direct current of a magnitude proportional to the value received. Each of these direct currents is passed through a fixed resistance IOI, and thus the potential drop across said resistance I0! is proportional to the received value, i. e. Ekr/cos A uniformly wound resistance I02 of arcuate form is located adjacent each ring I00 and is engaged by means of a sliding contact I03 mounted on said ring. Said resistance I02 is connected across a source of power I04, and one end of said resistance I02 is connected through a galvanometer I05 to an end of the resistance IOI, while the sliding contact I03 is connected to the-other end of said resistance IN, The direction of the currents through the resistances IM and I02 respectively are such that the voltage drop across the resistance IN is opposed to the voltage drop between the contact I03 and the end or the resistance I02 whichis connected through the galvanometer I05 to said resistance IOI. If these voltage drops are unequal, the needle 01' the 89.1- vanometer I05 will move in one or other direction from zero and this will move a switch I09 in one or other direction so as to connect across a source of power I01 for movement in one or other direction, a. reversing motor I09 which is adapted to drive the ring I00. The arrangement is such that, if the said voltage drops do not balance, the motor I09 will move the ring I00 in such a direction as to cause them to balance.

The arrangement is such that, when no value is received by the telereceiver 99 the voltage drop across the resistance IN is equal to hall that across the resistance I02. Therefore when no value is received by said telemeter receiver 99 the contact I03 will take up a position at the centre of the resistance I02. This is the normal or central position of the ring I00 hereinbeiore referred to. For positive values received by said receiver 99 (i. e. when the corresponding station bus bar is sending out power) the voltage drop across the resistance IOI is increased and the contact I09 will therefore move towards the right hand end of the resistance I02 and the resistance value of the rheostat 12 will be diminished, and as the winding of the resistance I92 is uniform the displacement of the ring I99 and resistance 12 will be proportional to the value of Bier/cos" Obviously for negative valuesreceived by the receiver 99 the ring I99 and resistance I2 will be displaced in the opposite, or resistance increasing direction by the said value Bier/cos c. As will have been clear from the description relating to Figure 6 a diminution of the resistance I2 gives a decrease in the power sent out by the group of power units at the corresponding regional control station, and

vice versa.

If in the central position of the ring I99 and resistance I2 the position of the contact 13 was logic dzl/da: corresponding to a slope value of dy/aix of the input-output curve of the corresponding group or power units (the scale being based on the basis I9) then after the ring I99 has been rotated by the action of the telemeter receiver 99 the position of the contact I9 will become logic dy/dx-C zlcr/cos 4 which, for small values of the second term and choosing the arbitrary constant C' lOgm e=9.434, corresponds to a slope value of which is the value required for the slope of the characteristic curve of the respective group of power units in order, to obtain the most economic load distribution.

It might happen that a tile line should become overloaded. Figure 9 shows an arrangement whereby such overloading is prevented. Referring to this figure the busbars 94 (corresponding to those of Figure '7) of two regional control sta tions are shown connected by a tie line 96 (corresponding to those of Figure 'l) which for the sake of simplicity is shown as a single phase line. If the power which is required to be transmitted from one busbar to. the other by said tie line 96, for the condition of most economic load distribution should be in excess of the capacity of such tie line'96, then the regional power output at one busbar is reduced and that at the other correspondingly increased, to just such an extent as to reduce the actual power transmitted along the tie line 96 to a value which is within the capacity of said tie line. This is done in the following way:

The watt meters 91 (corresponding to the watt meters 91 of Figure '7) have sliding contact rheostats I99 connected in series with their pressure coils as indicated, and the sliding contacts I I9 of said rheostats are controlled by means of respective regulators I II connected in the circuit of the tie line 96. For normal loadings of said tie line 96 the regulators III are ineffective and the sliding contacts I I9 remain stationary at a given normal position and the wattmeters accordingly indicate the correct power values and the telemeter senders 99 (corresponding to the senders 99 of Figure '7) send the correct values to the telemeter receivers at the master control station (not shown in Figure 9). As soon as the power transmitted along the tie line 96 approaches overload value the regulators III commence to move the sliding contacts I I9 so as to decrease the resistance of the rheostats I99. This causes the wattmeters 91 to indicate an incorrectly great power transmission, and consequently the senders 99 send an incorrectly great value and the adjustment made to the rings I99 at the master control station (not shown in Figure 9) is incorrectly great. This has the effect as will be older of reducing the output to the busbar 96 which is transmitting to the tie line 99 and increasing the output to the busbar 94 which is receivingirom the tie line 96. The regulators III must of course have a certain range so as to be able to adjust the rheostats I99 gradually, and when the load in the tie line 96 begins to drop again the resistance values of the rheostats I99 will again increase, until, when said resistance value reach normal the regulators will cease to function again and the system will be working at the most economic load distribution Just as in Figures 7 and 8.

The same rheostats I99 can be emploped to make the manual adjustment to allow for varying value of cos 4:.

Obviously these adjustments, instead of being made to the circuits of the pressure coils of the wattmeters could be made at some point between said wattmeters 91 and the senders 99. This would have the advantage that the wattmeters would always indicate the correct values.

In the various embodiments of the invention heretofore described in the preceding description, the most eflicient load distributionbetween a number of energy transmission units supplying a common load is obtained. This, however, presupposes that all the units are in use. The principle heretofore described, that the units should all work on points of their characteristic curves which are of the same slope, cannot be used to determine how many and which units ought to be employed for greatest efflciency for any given total load, because the said principle ignores the relative positions of the several characteristic curves, or, what amounts to the same thing, it does not take into account the no-load input required. It might well be, particularly when the load varies over a wide range, that, for difierent loads, better eiliciency is obtained if different selections of less than all of the units are employed, the remainder being cut out altogether. In Figures 19, 11 and 12 means are described for automatically determining which units are to be employed for maximum eiiiciency fOr any given total load.

It will be appreciated that, for a given number n of units, the number of possible combinations which may be emploped is 2"l. For example if there are three units a, b and c the number of possible combinations will be 2 1=7. These combinations may, for the sake of clarity, be set out as follows: a alone, b alone, 0 alone, a+b. a-I-c, b+c, and a+b+c.

If now the 2 1 characteristic curves (i. e. input-load curves) of the total possible combinations of units are plotted on one sheet, these curves will together build up a single enveloping curve which will be the curve of maximum efliciency for the whole set of units and will show which combination should be worked on for maximum efiieiency for any given total load.

In calculating the characteristic curves for the different combinations of units, the units of the combinations are of course assumed to have their loads distributed according to maximum efliciency. That is they are assumed to work as described in the various preceding examples, on points of their individual characteristic curves which are of the same slope.

tic curve for the unit a; the curve B is the characteristic curve for the unit b, and the curve AB is the characteristic curve for the units a and b together. It will be seen that these curves together build up an enveloping curve which consists partly of the curve A, partly of the curve B and partly of the curve AB. This curve is to be worked on for best efficiency. For certain output values, the part of the enveloping curve to be worked on is the part consisting of A alone, and this means that for these output values the unit a should be employed alone. For other output values the part of the enveloping curve to be worked on its the part consisting of B alone, means that for such output values the unit I) alone should be employed, and for other output values, the part of the enveloping curve to be worked on its the part AB means that for such output values both units a. and b should be employed together. Of course it might be found that the curve A or the curve B never appeared on the enveloping curve at all and this would simply mean that the unit a or the unit b are never to be used alone. In like manner, in larger installations, there might be many combinations of units Whose curves would never appear on the enveloping curve and which would therefore never be required.

A simple way to eifect practical control of the cutting in and out of the units according to the requirements indicated by Figure 10 is illustrated in Figure 11. In this figure three cams H2, H3, and H4 corresponding respectively to the three curves A, B and AB are mounted on a common rotatable cam shaft I I5. Thus the angular positions of the radii of each cam represents the load ordinates of the respective characteristic curve, and the radii themselves represent negatively the input ordinates of said curve. By the expression negatively" it is to be understood that, the less the input ordinate the greater the radius. It will be seen that the profile of this combination of cams, looked at in a direction axially of the shaft, will represent the aforesaid enveloping curve, each cam portion which, for any given angular range, has the greatest radius of the set, forming part of said enveloping curve.

The three cams have associated rollers I I6, I I1 and H8 mounted on a common bar II9 parallel to the cam shaft I I and which while remaining parallel to said cam shaft I I3, is capable of moving in a plain which is radial with respect to said cam shaft. This bar IIS is biased by means of springs I20 towards the cam shaft H5 and it will be seen that said shaft will come to rest with one of the rollers engaging with its respective cam. The cam shaft H5 is rotated in accordance with the total load, according to the same scale which determines the angular positon of the cam radii and it will therefore be seen that, assuming the angular positon of the radial plane of reciprocation of the bar II9 to be correctly located, for any given load, whichever roller is in contact with its respective cam determines which unit or combination of units is to be worked. In Figure 11 for example the angular position of the cam shaft I I5 is such that the roller I I1 is in engagement with its cam H3 and this shows that for the total load represented by the said angular position the unit b alone should be worked.

As stated the angular position of the cam shaft I I5 is adjusted automatically in accordance with the total load. The units are also cut in and out automatically according to the requirements indicated. This is done electrically in the following manner:

The bar H9 and its rollers H6, H1 and II! are of metal and said shaft has a common terminal I2I mounted on it. The cams H2, H3 and I II are also of metal but they are insulated from each other. Such cams are formed with respective associated bosses I22, I23 and I24 (not seen) and respective leaf spring contacts I25, I26, and I2! engage with the peripheries of these bosses. These leaf spring contacts are mounted on a common insulating base I28 for the whole structure and have associated terminals I29, I30 and I ll.

It wil be seen that when the unit a alone is required, electrical connection will be established from the terminal I2I to the terminal I29 said connection being by way of the shaft II9 the roller II6 the cam II2 the boss I22 and the leaf spring contact I25. In similar manner when unit b alone is required, connection is established from said terminal I2I to the terminal I30 and when units a and b are required together, connection is established from said terminal I2I to the terminal I3I.

Referring now to Figure 12 the references I32, I33 designate automatic starters for the units a and b respectively. Each of these starters when energised does everything necessary to start its respective unit, and, when de-energised to stop its respective unit. The energisation of these starters is controlled by means of relays aI, bI having normally open contacts as will be clear from the diagram.

The references AI BI designate normally closed contacts which are operated by the respective units a and b in such a way that they open when the respective units are in full operation.

The references a2, b2 designate respective relay windings. The winding a2 has normally closed contacts 112 and the winding b2 has normally closed contacts b2 and b2.

The reference cl designates the winding of a relay having normally open contacts cI and cI Figure 12 also shows the terminals I2I, I29, I30 and III of the preceding figure.

Assuming that the roller H6 is in engagement with its cam II2 so that terminal I2I is connected to terminal I29, and that only the unit a is in operation, the condition will be that the contact BI will be closed and the winding aI accordingly energised, and the starter I32 energised for operating the unit a. The winding a2 will also be energised causing the contacts (12 to open but this will be for the moment without efiect as the terminals I30 and I2I are disconnetted. As the winding 172 is de-energised the contacts 122 and D2 are both closed but without eflect as the contacts b2 only parallel the contacts BI, and the contacts b2 cannot establish the circuit of CI as the terminals I2I and Ill are disconnected.

It now the total load increases until the point is reached where the rollers H6 and II! are both in engagement with their respective cams so that the terminal I2I is connected simultaneously to 'both terminals I29 and I30 the relay winding b2 will be energised, and the contacts b2 and 172 will open, but this will be for the moment without effect, and the unit a alone will accordingly remain in operation.

If. now the total load is increased further so that the roller vIIS disengages the cam II2 the roller III remaining in engagement with the cam II! the terminal I29 will be disconnected from the terminal I2I and the winding a2 will be deenergised, causing the contacts 112 to close. The winding bl will accordingly be energised, energising in turn the starter I33v and starting the unit b. The unit a will, however, continue operating for a short time until the unit b is fully in operation whereupon the contact bl will open and the winding aI will be de-energized, thereby de-energising the starter I32 and putting the unit a out of operation. The unit I) alone will now be in operation. Also the contact AI will close affording an altemative path of energisation for winding bl.

If now the total load is increased still further so that the rollers I I1 and H8 both engag their respective cams, and the terminals I and I1 are both connected to the terminal I2I nothing further will take place because the contacts M are open as heretofore stated. The unit b therefore remains alone in operation.

If now the total load increases still further so that the roller Ill disengages the cam .II3, the roller IIB remaining in engagement with the cam H4 the terminals I2I and I30 are disconnected from each other and the relay winding I)! is de-energised thereby closing the contacts b2 and Z12 Closing of contacts b2 will be without effect; closing of contacts 172 will effect energisation of the winding cl and consequent closing of the contacts cl and cI The windmg M will be energised thereby opening the contacts b2 and de-energising the winding cI. The contacts cI and cI will accordingly both open. Opening of contact cI will de-energise winding at and put the unit a cut. of operation, but the opening of contacts cI will not deenergise the winding bl because the contacts (12 are closed as the winding a2 is de-energised. The unit I) will accordingly alone remain in operation. Owing to the unit a ceasing to operate, the contacts at will close affording an alternative path of energlsation for winding bl.

Since the a and b circuits are symmetrical with respect to one another, the operation, as the total load continues to decrease, will be exactly the converse, in changing from the unit I) alone to the unit 1: alone, to the heretofore described operation in changing from the unit a alone to the unit b alone when the total load was increasing. deemed necessary.

It will be clear that, in al1 of the arrangements heretofore described except Figures 7, 8 and 9, the controlling mechanism instead of actually controlling the load distribution of the several power units, could be used to indicate the required load distribution of said power units. Thus the rods 3 of Figure 1 or sliding contacts 50 of Figure 4 or the windings aI, bI of Figure 12 instead of actually controlling the respective power unit could operate an indicating device which would indicate the control of the respective power unit required, the said control being afterwards efiected by hand.

Further description is therefore not etc. etc. or indeed to plants outside the sphere of confined to the control of steam generators and Further the whole control system could be physically disassociated from the comon load and the adjustment of the handle 20 in the case of Figures 1 and 2 or the handle 20a in the case of Figure 3 or the shaft 5I in the case of Figure 4 or the shaft 14 in the case of Figures 5 and 6 or the shaft II5 of Figure 11 could be adjusted by hand in accordance with the total output required or the frequency as the case may be. Those of the appended claims which relate to any of Figures 1 to 6 or 10 to 12 are deemed to cover such arrangements.

In the case, however, of Figures 7, 8 and 9 this is not possible, as the modification of the load distributor in accordance with tie line losses depends on reaction within the net work itself. If in this case, an indicating, instead of an actual controlling device is required, this could only be done by employing an electrical model of the actual network.

By impressing on the circuits representing the stations, regional costumers, and tie-lines, potentials or phase angles proportional to the allocated output, the resulting potential or phase differences will cause currents to flow between the points representing the several stations. These currents which are analogous to the energy flow in the actual network may then be used to shift the several rheostats of the indicating device as described in the specification. Those of the appended claims which relate to Figure 7, 8 or 9 are deemed to cover such an arrangement.

It will be appreciated that the invention is not electrical power generators. The invention can be applied to any units of similar or dissimilar character operating in parallel if their inputs and outputs can be expressed in the same terms respectively. The invention can, for example, be applied to the parallel operation of different power stations, either thermal or hydraulic or both, or to pump works, grinding mills, steam engines,

engineering.

What I claim and desire to secure by Letters Patent is: I

1. A system of control of the load distribution of a plurality of energy-transmission units supplying a given system, comprising a common ele ment, means for actuating said common element in accordance with a condition of the said system, individual controlling devices for effecting the control of the several units, means whereby said controlling devices are-actuated jointly by said common element in such a Way that said condition is regulated and said units operate to give maximum combined output relative to their combined input, said means being provided with elements shaped in accordance with the logarithms of the slopes of the input-output curves of the several energy-transmission units whereby the input values of any one of said energy-transmission units in relation to their respective output values may be modified in accordance with the logarithm of a predetermined factor K.

2. A system of control of the load distribution of a plurality of energy-transmission units supplying a given system, comprising a common element, means for actuating said common element in accordance with a condition of the said system, individual controlling devices for effecting the control of the several units and means whereby said controlling devices are actuated jointly by said common element in accordance with the logarithms of the slopes of the input-output characteristic curves of the several units so that said condition is regulated andsaid units operate at points on their input-output characteristic curves where the logarithms of the slopes are equal.

3. A system or control 01' the load distribution of a plurality of energy-transmission units supplying a given system, comprising a common element, means for actuating said common element in accordance with a condition 01 the said system, individual controlling devices for effecting control of the several units, and means whereby each or said controlling devices are actuated jointly by said common element in accordance with the logarithms oi the slopes of the inputoutput characteristic curves of the respective units so as to tend to maintain said conditions constant, while, at the same time, said units operate to give maximum combined output relative to their combined input.

4. A system of control of the load distribution of a plurality of energy-transmission units supplying a given system, comprising a common element, means for actuating said common element in accordance with a condition of the said system, individual transmission devices actuated jointly by said common element for effecting control oi the inputs of the several units solely in accordance with the position of said commonelement in such a sense as to regulate said condition, said transmission devices being so formed and correlated that said units operate to control said energy-transmission units in accordance with and at equal values of the logarithms of the slopes of the input-output characteristic curves of the respective energy-transmission units.

5. A system of control of the load distribution 01' a plurality of energy-transmission units supplying a given system, comprising a plurality oiparts formed to represent the input-output characteristic curves of the respective units, a plurality of parts formed to represent straight lines, means for correlating the second named parts respectively to the first named parts in such a way that the straight lines oi said second named parts are always tangent to the curves of the first named parts, means for coupling said second named parts together in such a way that their straight lines always remain parallel to each other, means for jointly rotating said second named parts relatively to said first named parts in accordance with variations in a condition of said system, controlling parts movable in accordance with the components of the movements oi the respective tangent points of the curves of the first named parts and the straight lines o! the second named parts, which components are parallel to ordinates of said curves of the first named parts, and means for controlling the inputs oi the respective units in accordance with the movements or said controlling parts in such a way as to regulate said condition and to cause the re- & spective units to work on points of their characteristic curves corresponding to the said tangent points of the curves of the first named parts and the straight lines of the second named parts.

6. A system of control of the load distribution 01' a plurality of energy transmission units supplying a given system, comprising a plurality oi parts formed with slots representative the input-output characteristic curves of the respective units, a plurality of parts formed with straightline slots, a roller engaging Jointly in the slots of each corresponding curved and straight-line pair, and co-engaging curved and straight-line surfaces or each corresponding pair oi first named and second named parts, which, together with said roller, ensure that the straight-line slot is always tangent to the-curved slot at the point occupied by said roller, means for coupling the second named parts together, in such a way that their straight-line slots always remain parallel to each other, means for Jointly rotating said second named parts relative to said first named parts in accordance with variations in a condition oi said system, controlling parts movable in accordance with components oi the movements 0! the respective rollers, which components are parallel to ordinates of said curved slots, and means for controlling the inputs 0!. the respective units in accordance with the movements of said controllingpartsinsuchawayastoregulatesaidcondition and to cause the respective units to work on points oi. their characteristic curves corresponding to the positions 0! said rollers on said curved slots. I

7. A system of control or the load distribution ot a plurality oi energy transmission units supplying a given system, comprising a common element, means for actuating said common element in accordance with a condition of the said system, individual controlling devices for efiecting the control of the several units and means whereby said controlling devices are actuated Jointly by said common element in such a way that said condition is regulated and said units normally all operate on points of their input-output characteristic curves which are oi the same slope, but that if the demand increases (or decreases) when any unitis already operating at maximum (or minimum) load, said unit remains at its maximum (or minimum) load and the remaining units operate on points or their input-output characteristic curves which are of the same slope,

8. A system of control oi the load distribution of a plurality oi energy transmission units supplying a given system, comprising a plurality 01' parts formed to represent the input-output characteristic curves of the respective units, a plurality 01' parts formed to represent straight lines, means for correlating the second named parts respectively to the first named parts in such a way that the straight lines of said second named parts are always tangent to the curves of the first named parts save when any straight line touches the extreme point of the corresponding curve when it is'capable of rotating about said extreme point, means for coupling said second named parts together in such a way that their straight lines always remain parallel to each other, means for Jointly rotating said second-named parts relatively to said first named parts in accordance with variations in a condition of said system, controlling parts movable in accordance with the components or the movements or the respective points of contact of the curves oi the first named parts and the straight lines of the second named parts, which components are parallel to ordinates of said curves of the first named parts, and means for controlling the inputs -01 the respective units in accordance with the movements of said controlling parts in such a way as to regulate said put-output characteristic curves of the respective units, a plurality of parts formed with straight-line slots, a roller engaging Jointly in the slots of each corresponding curved and straight-line pair, and co-engaging curved and straight-line surfaces of each corresponding pair oi. first named and second named parts, which, together with said roller, ensure that the straightline slot is always tangent to the curved slot at the point occupied by said roller, save when any straight-line slot touches the extreme point of the corresponding curved slot when it is capable of rotating about the corresponding roller at said extreme point, means for coupling the second named parts together in such a Way that their straight-line slots always remain parallel to each other, means for jointly rotating said second named parts relative to said first named parts in accordance with variations in a condition of said system, controlling parts movable in accordance with components of the movements of the respective rollers, which components are parallel to ordinates of said curved slots, and means for controlling the inputs of the respective units in accordance with the movements of said controlling parts in such a way as to regulate said con dition and to cause the respective units to work on points of their characteristic curves corresponding to the positions of said rollers on said curved slots.

10. A system of control of the load distribution of a plurality of energy-transmission units supplying a given system, comprising a common e1emerit, means for actuating said common element in accordance with a condition of the said system, and individual cam transmission devices actuated jointly by said common element for plying a given system, comprising a common cam shaft, means for rotating said cam shaft in accordance with a condition of said system, individual cams mounted on said cam shaft, the radii of each cam representing ordinates, and the angular positions of said radii representing the slopes corresponding to said ordinates, of the input-output characteristic curve of the respective unit, respective controlling parts engaging with, and movable by, the peripheries of said cams as the cam shaft rotates, and means for controlling the inputs of the respective units in accordance with the movements of said controlling parts in such a way as to regulate said condition and to cause the respective units to be regulated in accordance with equal logarithms of the slopes of the input-output characteristic curves of the respective units.

12. A system of control of the load distribution of a plurality of energy-transmission units supplying a given system, comprising a common cam shaft, means for rotating said cam shaft in accordance with a condition of said system, individual cams mounted on said can shaft, said cams being so shaped as to correspond to and be in accordance with the logarithms of the slopes of the input-output characteristics of the respective energy-transmission units, and the radii of certain of said cams from a point representing an extremity of the respective input-output char acteristic curve remaining constant, respective controlling parts engaging with, and movable by, the peripheries of said cams as the cam shaft rotates, and means for controlling the inputs of the respective units in accordance with the movements of said controlling parts in such a way as to regulate said condition and to cause the re spective units to work on points of their characteristic curves corresponding to the points of contact of said controlling parts with the peripheries of said cams.

13. A system of control of the load distribution of a plurality of steam generators supplying a common supply pipe, comprising a common element, means for actuating said common element in accordance with the pressure in said common supply pipe, individual controlling devices for effecting the control of the several steam generators and means for actuating said controlling devices whereby they are actuated jointly b said common element in such a way that the pressure in said common supply pipe is regulated and said steam generators operate to give maximum combined output relative to their combined input in accordance with equal logarithmic values of the slopes of the input-output characteristic curves of said individual generators.

14. A system of control of the load distribution of a plurality of electrical generator sets supplying a common system, comprising a common element, means for actuating said common element in accordance with the frequency in said common system, individual controlling devices for effecting the control of the several electrical generator sets in accordance with the logarithm of the slopes of the input-output characteristic curves thereof, and means whereby said controlling devices are actuated jointly by said common element in such a way that the frequency in said common system is regulated and said electric generator sets operate to give maximum combined output relative to their combined input.

15. A system of control of the load distribution of a plurality of energy-transmission units supplying a common system, comprising a common element, means for actuating said common element in accordance with a condition of said system, a plurality of sliding contact rheostats each so wound that, if the position of its sliding contact represents the logarithm of the slope of the input-output characteristic curve of the respective energy-transmission unit, the resistance of said rheostat is a function of said logarithm of the slope of said characteristic curve, means for actuating said sliding contacts jointly by said common element in such a way that the logarithms represented by the positions of said sliding contacts are always the same and means for controlling the inputs of said energy-transmission units according to the resistances of the respective rheostats in sucha way as to regulate said condition and to cause the respective units to work on points of their characteristic curves corresponding to the positions of the respective sliding contacts.

16. A system of control of the load distribution of a plurality of energy-transmission units supplying a common system, comprising a plurality of sliding contact rheostats each so wound that, if the position of its sliding contact represents the slope of the input-output characteristic curve of the respective energy-transmission unit, the resistance of said rheostat is a function of an ordinate of said characteristic curve corresponding to said slope, a common shaft on which said sliding contacts are mounted, the slopes represented by the position of said sliding contacts being always the same, means for rotating said common shaft in accordance with a condition of said system and means for controlling the inputs of said energy-transmission units according to the resistances of the respective rheostats in such a way as to regulate said condition and to cause the respective units to work on points of their characteristic curves corresponding to the positions of the respective sliding contacts.

17. A system of control of the load distribution of a plurality of energy-transmission units supplying a common system, comprising a common element, means for actuating said common element in accordance with a condition of said system, a plurality of sliding contact rheostats each so wound that, if the position of its sliding contact represents the slope of the input-output characteristic curve of the respective energytransmission unit, the resistance of said rheostat is a function of an ordinate of said characteristic curve corresponding to said slope, means for actuating said sliding contacts jointly by said common element in such a way that the slopes represented by the positions of said sliding contacts are always the same, means for controlling the inputs of said energy-transmission units according to the resistances of the respective rheostats in such a way as to regulate said condition and to cause the respective units to work on points of their characteristic curves corresponding to the positions of the respective sliding contacts and means whereby, when certain of said sliding contacts is moved beyond the point of its resistance representing an extremity of the input-out put characteristic curve the value of said resistance remains constant.

18. A system of control of the load distribution of a plurality of energy-transmission units supplying a given system, comprising a common element, means for actuating said common element in accordance with a condition of the said system, individual transmission devices actuated jointly by said common element for effecting control of the inputs of the several units in accordance with the position of said common element in such a sense as to regulate said condition, the movement of said transmission devices at their input ends representing the slopes of the characteristic curves of the respective units according to a logarithmic scale, and the movements of said transmission devices at their output ends representing ord nates of said characteristic curves corresponding to said slopes, and the joint movement of said transmission devices at their input ends being such as to correspond to the same slope for all the devices, and means whereby the inputs of said units are controlled by the movements of said transmission devices at their output ends in such a way as to ensure that said units shall operate on points of their characteristic curves represented by the positions of the respective transmission devices.

19. A system of control of the load distribution of a plurality of energy-transmission units supp'ying a given system, comprising a common cam shaft, means for rotating said cam shaft in accordance with a condition of said system, individual cams mounted on said cam shaft, the radii of each cam representing ordinates, and the angument in accordance with a condition ofsaid syslar positions of said radii being proportional to the logarithms of the slopes corresponding to said ordinates, of the input-output characteristic curve of the respective unit, respective controlling parts engaging with, and movable by, the peripheries of said cams as the cam shaft rotates, and means for controlling the inputs of the respective units in accordance with the movements of said controlling parts in such a way as to regulate said condition and to cause the respective units to work on points of their characteristic curves corresponding to the points of contact of said controlling parts with the peripheries of said cams.

20. A system of control of the load distribution of a plurality of energy-transmission units supplying a given system, comprising a common cam shaft, means for rotating said cam shaft in accordance with a condition of said system, individual cams mounted on said cam shaft, the radii of each cam representing ordinates, and the angular positions of said radii being proportional to the logarithms of the slopes corresponding to said ordinates, of the input-output characteristic curve of the respective unit, respective controlling parts engaging with, and movable by the peripheries of said cams as the cam shaft rotates, and means for controlling the inputs of the respective units in accordance with the movements of said controlling parts in such a way as to regulate said condition and to cause the respective units to work on points of their characteristic curves corresponding to the points of contact of said controlling parts with the peripheries of said cams and means whereby the angular position of certain of said cams on said shaft is adjustable.

1. A system of control of the load distribution of a plurality of energy-transmission units supplying a common system, comprising a common element, means for actuating said common eletem, a plurality of sliding contact rheostats each so wound that, if the position of its sliding contact varies as the logarithm of the slope of the input-output characteristic curve of the respective energy-transmission unit, the resistance of said rheostat is a function of an ordinate of said characteristic curve corresponding to said slope, means for actuating said sliding contacts Jointly by said common element in such a way that the slopes represented by the positions of said sliding contacts are always the same, and means for controlling the inputs of said energy-transmission units according to the resistances of the respective rheostats in such a way as to regulate said condition and to cause the respective units to work on points of their characteristic curves corresponding to the positions of the respective sliding contacts.

22. A system of control of the load distribution of a plurality of energy-transmission units supplying a common system, comprising a common element,'means for actuating said common element in accordance with a condition of said systerm, a plurality of sliding contact rheostats each so wound that, if the position of its sliding contact varies as the logarithm of the slope of the input-output characteristic curve of the respective energy-transmission unit, the resistance of said rheostat is a function of an ordinate of said characteristic curve corresponding to said slope, means for actuating said sliding contacts Jointly by said common element in such a way that the slopes represented by the positions of said sliding contacts are always the same, means for controlling the inputs of said energy-transmission units according to the resistances of the respective rheostats in such a way as to regulate said con-' dition and to cause the respective units to work on points of their characteristic curves corresponding to the positions of the respective sliding contacts, and means whereby the resistance elements of certain of said rheostats are longitudinally adjustable.

'23. A system 01' control of the load distribution of a plurality of energy-transmission units supplying a given system, said units being divided into groups, comprising a group-control element for each group, individual controlling devices for eifecting the control of the several units, means whereby the individual controlling devices of each group are actuated Jointly by the group-control element of said group in such a way that the units of the group operate to give maximum combined output relative to their combined input, a master control element, means whereby said group control elements are actuated jointly by said master control element in such a way that the several groups, taken as a whole, operate to give maximum combined output relative to their combined input, and means for actuating said master control element in accordance with a condition of the system supplied in such a sense that said condition is regulated.

24. A system of control of the load distribution of a plurality of energy-transmission units supplying a given system, said units being divided into groups, comprising a group-control element for each group, individual controlling devices for efiecting the control of the several units, means whereby the individual controlling devices of each group are actuated jointly by the group-contro element of said group in such a way that the units of the group operate on points of their characteristic curves which are of the same slope, a

master control element, means whereby said group control elements are actuated jointly by said master control element in such a way that the several groups, taken as a whole, operate on points of their group characteristic curves which are of the same slope and means for actuating said master control element in accordance with a condition of the system supplied in such a sense that said condition is regulated.

25. A system of control of the load distribution of a plurality of energy-transmission units supplying a given system, said units being divided into groups, comprising a group-control element for each group, individual controlling devices for effecting the control of the several units, means whereby the individual controlling devices of each group are actuated jointly by the group-control element of said group in such a way that the units of the group operate on points of their characteristic curves which are of the same slope, a master control element, means whereby said group control elements are actuated jointly by said master control element in such a way that the several groups, taken as a whole, operate on points of their group characteristic curves which are of the same slope, means for actuating said master control element in accordance with a condition of the system supplied in such a sense that said condition is regulated, and means located at the region of the master control element for indicating the total output of the whole system.

26. A system of control of the load distribution of a plurality of energy-transmission units supp ying a common system, comprising a common element, means for actuating said common element in accordance with a condition of said system, a plurality 01' sliding contact rheostats each represented by the positions of said sliding contacts are always the same, means for controlling the inputs of said energy-transmission units according to the resistances of the respective rheostats in such a way as to regulate said condition and to cause the respective units to work on points of their characteristic curves corresponding to the positions of the respective sliding contacts, said last named means comprising means for passing a constant current through said rheostats in series and means for controlling the inputs to said energy-transmission units according to the voltage drops across the respective units, and comprising in addition means for measuring the total voltage drop across said rheostats and thereby measuring the total output of the whole system.

27. A system of control of the load distribution of the plurality of groups of energy-transmission units supplying a common system, comprising a master control element, means for actuating said master control element in accordance with a condition of said system, a plurality of sliding contact rheostats each so wound that, if the position of its sliding contact represents the slope of the input-output characteristic curve of the respective group of energy-transmission units taken as a whole, the resistance of said rheostat is a function of an ordinate of said characteristics curve corresponding to said slope, means for actuating said sliding contacts jointly by said master control element in such a way that the slopes represented by the positions of said sliding contacts are always the same, means for controlling the inputs of said roups of energy-transmission units according to the resistances of the respective rheostats in such a way as to regulate said condition and to cause the respective groups of units to work on points of their characteristic curves corresponding to the positions of the respective sliding contacts, said last named means comprising means for passing a constant current through said rheostats in series and means for controlling the inputs tosaid groups of energy-transmission units according to the voltage drops across the respective units, and means for measuring the total voltage drop across said rheostats and thereby measuring the total output of the whole system.

28. A system of control of the load distribution of a plurality of electrical generator stations supplying a common system, and in which the outputs from the several stations are inter-connected 

